Roving is produced from slivers, which are usually pretreated (for example, doubled) by drafting and serves as the precursor for the subsequent spinning process, in which the individual fibers of the roving are spun, for example by means of a ring spinning machine, to form a fiber yarn. In order to give the roving the strength necessary for the further processing, it has proven to be advantageous, during production of the roving, to draft the supplied fiber bundle by means of a drafting system, which is usually part of the spinning preparation machine in question, and then to provide it with a protective twist. The aforementioned strength is important in order to prevent the roving from breaking during the winding onto a tube and/or during the feeding thereof to the downstream spinning machine. The applied protective twist must, on the one hand, be strong enough to ensure that a cohesion of the individual fibers during the individual winding and unwinding processes and corresponding transport processes between the respective types of machine is ensured. On the other hand, it must also be ensured that, despite the protective twist, the roving can be further processed in a spinning machine—the roving must therefore still be able to be drafted.
For producing such a roving, so-called flyers are preferably used, the delivery speed of which is nevertheless limited due to centrifugal forces that occur. There have therefore already been many proposals for circumventing the flyers or replacing them with an alternative type of machine (see, for example, EP 0 375 242 A2, DE 32 37 989 C2).
In this connection, it has also already been proposed, inter alia, to produce roving by means of air-jet spinning machines, in which the protective twist is created by means of airflows. The basic principle here consists in guiding a fiber bundle through a vortex chamber, in which an air vortex is generated. The latter finally effects that some of the outer fibers are wrapped as so-called wrapping fibers around the centrally extending fiber strand, which in turn consists of core fibers extending substantially parallel to one another.
Since the production of a roving fundamentally differs from the production of a conventional yarn (because yarn and roving differ significantly in terms of strength and draftability), it is not possible to use known air-jet spinning machines to produce a roving. Rather, the dimensions and/or geometry of the spinning station of a spinning preparation machine must be selected independently of the known prior art.